Future models could also include sensors to monitor blood oxygen saturation and core body temperature

Some Bluetooth headsets are designed to get beats into your ear: The C-SP 01 from Cosinuss is there to get them out.

Cosinuss is showing a prototype of the device -- it's a heart-rate monitor, not a headphone -- at the Cebit trade show in Hanover this week, as part of the Code_n startup competition.

Instead of a loudspeaker, the earpiece contains a sensor that can measure heartbeats optically, detecting the rush of blood under the skin inside the ear. It's based on the same principle as the fingertip heart-rate monitors used in hospitals.

Future versions will also be able to measure core body temperature and, with the addition of another LED and photodiode to the sensor pack, blood oxygen saturation too, said CFO Greta Kreuzer. To meet the deadlines of the Code_n competition, however, the prototype on show only contains the pulse sensor, she said.

The case containing the micro-USB recharging socket and the battery fits behind the ear. It also houses the electronics that track the arrival of each surge of blood in the vessels beneath the skin, deciding at what moment to count a heartbeat, and calculating the heart rate from that.

The heart-rate monitor can transmit information to smartphones that support the Bluetooth Low Energy standard, or to devices with an ANT+ interface. ANT+ is an ultra-low-power wireless protocol supported by many health and fitness monitoring devices, and also by the Galaxy S4 and S5 smartphones from Samsung Electronics.

Cosinuss is aiming to bring the product to market in the fourth quarter, with a target retail price of a!150 (US$208), Kreuzer said. At least for now, it will leave app development to other companies: There are already plenty out there that can log and chart the heart rate data it produces, associating it with work-out diaries or even GPS traces.

While its first product will be a fitness accessory, the company's sensor system also has other applications including health care and occupational safety, monitoring the health of workers in dangerous environments, she said.

It could even be used for executive coaching, as a means of tracking stress, she said. Others have already used conventional sports heart-rate monitors with electrodes incorporated in chest bands for this purpose, she said, but with variable success, as the electrodes typically rely on perspiration to obtain sufficient conductivity to function.

An in-ear sensor is more practical, more comfortable and more reliable, she said.

Since we only have two ears into which we can insert such devices, a logical step would be to build the sensor into a mobile phone hands-free kit or a set of Bluetooth stereo headphones. The Cosinuss team is concentrating on building its own fitness device for now, Kreuzer said, but it could consider licensing its technology to enter other markets.